This application relates to an air turbine starter, and more particularly to airflow control for an air turbine starter.
Gas turbine engines are known and typically include a fan delivering air into a bypass duct for propulsion. The fan also delivers air into a compressor where air is compressed and delivered into a combustor. The air is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. The turbine rotors, in turn, rotate compressor rotors and the fan rotor.
An air turbine starter is typically included with a gas turbine engine for starting the gas turbine engine. The air turbine starter receives pressurized air from an auxiliary power unit when it is desired to start a gas turbine engine. The air turbine starter is connected to drive a compressor section of the gas turbine engine. When the air turbine starter receives the pressurized air, its turbine is driven to rotate, to in turn start rotation of the compressor section in the gas turbine engine through “motoring.”
Some gas turbine engines exhibit a so-called “bowed rotor” condition whereby certain components exhibit different thermal expansion from engine use, causing a shaft of a gas turbine engine, such as the “N1” shaft that interconnects a fan, low pressure compressor, and low pressure turbine of the gas turbine engine, or “N2” shaft that interconnects a high pressure compressor and high compressor turbine, to become bowed.
Starting up and idling an engine exhibiting a bowed rotor condition without sufficiently cooling the engine is undesirable, because rotor blades may not be properly centered and may excessively rub into a housing. This poses challenges for aircraft with short turnarounds between flights, because a gas turbine engine may take several hours of standstill cooling to fully resolve a bowed rotor condition.
Low speed motoring of a gas turbine engine exhibiting a bowed rotor condition at sub-idling rotational speeds is a method to shorten the time needed for cooling.